Melatonin is a hormone secreted by the pineal gland that controls seasonal and circadian hormonal rhythms, and alters the metabolism of testosterone and enhances the availability of estrogen receptors in target tissues.
Since the isolation of melatonin in 1959, reports of its ability to inhibit luteinizing hormone (LH) secretion with control of fertility led researchers (Flaugh et al., 1978) to investigate the action of melatonin analogs on plasma half life to produce compounds with the same biological activity as malatonin but with a prolonged serum half-life.
Schloot et al have determined that patients suffering from psoriasis have a severe disorder of melatonin secretion. Treatment with psoralen for rising the serum melatonin concentration of the patient is suggested. They suggested that the antimitotic effect of melatonin may be of importance for the regulation of increased epidermal mitotic rate and decreased cell turnover time.
Houssay et al (1966) (1) have shown that the pineal gland and the parenteral administration of melatonin acts on the skin of mice to slow hair growth waves in mice.
Houssay et al (1966) (2) describe that the parenteral treatment of mice with melatonin effects the hair growth waves in mice.
Rose et al (1984) have shown that it is possible to induce the growth of winter pelage in mink by implanting melatonin.
Logan et al (1980) have found that melatonin can inhibit in vitro melanogenesis in hair follicles of the Siberian hamster.
Heath et al (1982) have shown that follicular development was blocked in mice injected with melantonin.
Rats were used in the assay to measure effects on LH release and ovulation. Melatonin analogs were given p.o. and intravenously. Pronounced increase in activity and half-life was noted with halogenation on the 6 position.
Frohn et al (1980) reported a structural activity relationships between 23 indoleamines and melatonin utilizing an in vitro fish pigment bioassay. Indoles were dissolved in ethanol and given intraperitoneally. In this model, halogenation a 6- position and minor variations of the N-acyl group were without effect on comparable in vivo activity. Indole was found to be more active than melatonin. The 6-chloro-2,3-dihydromelatonin was believed to be a possible long acting melatonin agonist.
In a study of antagonists to the brain receptors for diazepam, melatonin and metabolites were tested to determine the inhibition of diazepam binding to rat synaptosomal membranes. Melatonin and its CNS metabolite N-acetyl 5-methoxy kynurenamine were found to be the most potent antagonists and beta carboline metabolites of melatonin were also noted as high affinity antagonists to diazepam (Marangos et al., 1981).
Rollag (1982) studied 18 different tryptophan derivatives, many of which are found in the pineal gland, to induce gonodal regression and aspermia in syrian hamsters. Only melatonin and 5-methoxy tryptamine were found to possess anti-gonadotrophin action. The action of 5-methoxytryptamine is supported in Pevet's review (1983) but melatonin is the most effective agent.
Similar studies were conducted by Richardson et al (1983), Vaughn et al (1983) with 6-chloromelatonin being the only analogue to possess anti-gonadotrophic activity equal to melatonin. Their paper reviews the structural activity literature evaluating melatonin analogues. This same group (Vaughan et al., 1982) explored the action of melatonin natural and synthetic analogues on the effects of cholesterol and thyroid levels in the male syrian hamsters as compared to melatonin. The native hormone melatonin was found to be the only structure lowering T.sub.4 (thyroxine) levels.
In a frog skin assay, Frohn, et al., (1980) concluded that the N-acetyl group attached to 3- position determines binding site affinity while the 5-methoxy group confers activity.
Melatonin and related metabolites were found to be the principal excretory products of the pineal gland (epiphysis cereberi), an endocrine organ present intracranially in all vertebrates (Reiter, 1983). In lower vertebrates there are true morphological photoreceptors present in the pineal gland but in mammals the pineal gland receives signals from neural sympathetic sources which effect the production of its principal secretory product melatonin (Reiter, 1983). The primary secretory route of melatonin in mammals is by way of the capillary bed of the gland itself (Rollag et al, 1977).
Melatonin (N-acetyl-methoxytryptamine) is primarily derived from tryptophan and synthesized via the action of tryptophane hydroxylase (Lovenberg et al., 1967). The pineal gland is the primary place for a major portion of physiological indolamine metabolism including that of the neuroeffector serotonin which is a major source of melatonin synthesis.
Melatonin synhesis is governed by light exposure and in man and other mammals and primarily produced in conjunction with night or in darkness from its pineal endocrine source. In addition to the pineal body, both the retina, the harderian gland (in rodents) and gastrointestinal tract are producers of melatonin (Ralph, 1981; Reiter et al, 1983: Raikhlin et al., 1975).
Besides melatonin, 5-methoxytopol (Wilson et al., 1978) and 5-methoxytryptamine (Pevet et al., 1983) are produced by the pineal and have been found to have endocrine effects.
The primary role of the pineal gland relates to its control of reproductive physiology (Tamarkin et al., 1985; Arendt et al., 1983; Stetson & Watson-Whitmyre, 1984). As mentioned previously, secretion of melatonin is governed by light to dark exposure of the animal and there are short day or long day seasonal breeding animals who are influenced differently by melatonin production governed by the seasonal light cycle.
An example of systemic melatonin effects on reproductive hormonal cycling are seen in the depression of testosterone production in mice given melatonin (Petterborg and Reiter, 1981). Alternatively, depending on species, testicular regression can be prevented and testosterone activity maintained (Turek, 1977; Stetson et al 1983) in hamsters. Melatonin, given by injection, can alter estrous cycling in female rats (Trentini, et al., 1980). Evidence supports the possibility that melatonin levels may be a factor in suppression of puberty in man (Tamarkin et al., 1985).
Melatonin is entering the commercial animal husbandry market to control fertility (breeding time), fur coat development and appetite. For example in ewes 2 mg/day, in pelleted feed, which mimics nocturnal blood levels, controls the estrous cycle and sheep fertility (Lincoln, 1983); (Kennaway et al., 1982). Similar effects on daily feeding have been observed in male white tailed deer (Bubenik, 1983) with earlier seasonal antler and coat changes.
Melatonin injected subcutaneously in saline or oil produces high transient blood levels while oral administration in saline or food pellets produces sustained blood levels (Kennaway and Seamark, 1980). Melatonin has been orally given in drinking water (Pevet and Haldar-Misra, 1982) or by subcutaneous slow release implants, i.e., sialastic (Turek, 1977; Losee and Turek, 1980; Kennaway and Gilmore, 1984) or by injection (Sisk and Turek, 1982).
The duration of melatonin exposure is significant since constant levels can produce refractoriness, thus intermittant exposure and the relation of melatonin to the animals photoperiod (light/dark cycle) is important (Stetson et al., 1983; Losee and Turek, 1980; Trentini et al., 1980; Stetson and Tay, 1983; Bittman, 1984; Tamarkin et al., 1985).
Melatonin injections can mimic syrian hamster short day photoperiod exposure with increases in body weight gain, feed efficiency, enhanced carcass lipid and brown adipose tissue mass and thermogenic capacity (Bartness and Wade, 1984).
The clinical use of melatonin in CNS disease has been reviewed by Anton-Tay (1974) and Romijn (1978) and there have been extensive studies of its intravenous, intrathecal and direct localized CNS implantation on behavior in a wide range of animal species that has led to clinical trial.
Waldhauser et al. (1984) have reviewed the clinical use of melatonin. They indicate that approxiamtely 150 subjects have received clinical melatonin intravenously or orally. In most cases, no significant toxicity was observed (Lerner and Norlund, 1978). As much as 3-6 gms of maltonin has been given orally daily for 1 month with reports of abdominal cramping and tranquilization (Papavasiliou, et al., 1972).
Melatonin has been given clinically to volunteers by mouth in carbowax at 1-25 ug/kg (Anton-Tay, 1974) or clinically to volunteers by mouth in corn oil as a 0.04% solution at a dose of 2 mg/day for 4 weeks (Arendt et al, 1984). It has been given orally in doses of 250 mg (Norlund and Lerner, 1977) and in doses up to 1.2 g/day (Anton-Tay, 1974; Carmen et al., 1976; Anton-Tay et al., 1971). These studies have demonstrated a systemic effect of melatonin with reports of melatonin induced fatigue and depression or sleep.
Melatonin has been given to human subjects in doses of 50 mg intravenously (Pavel et al., 1981; Cramer et al., 1974) where it induced sleep with normal or enhanced REM electroencephalographic patterns. Melatonin's sedative action has been confirmed by H. Lieverman, as cited by Walkhauser et al (1984), and are supported by the results of intranasal administration where melatonin, as a 0.85 percent ethanol spray induced sleep in 70 percent of patients within 40-60 minutes (Vollrath et al., 1981).
Melatonin has been studied p.o. and i.v. clinically in depression and in Huntington's chorea with no improvement or clinical worsening (Carman et al., 1976). In two patients with schizophrenia, I.V. melatonin (300 mg) worsened hallucinatory symptoms (Altschule cited by Carman et al., 1976).
In epilepsy, melatonin has produced some benefit on i.v. administration at a 1 percent solution in ethanol at dosages up to 1.25 mg/kg i.e. In Parkinsonism, given i.v. or p.o. for a daily total of 1.2 gms for 4 weeks (Anton-Tay et al., 1971), amelioration of tremor and rigidity have been seen although results have not been consistent in studies of Parkinsonism with all investigators as Papavasilou et al., 1972 has not seen benefit with doses as high as 6 gms daily. Carman et al. (1976) have reviewed the CNS clinical studies up to that time and the use of melatonin for the treatment of tremor and rigidity looked promising.
Melatonin has been given at dosages of 1 mg/kg i.m. with advanced breast cancer for periods up to 2 months. These studies were conducted after trial at 5 and 20 mg/kg i.m. daily for up to 10 days in monkeys with no report on clinical response other than a report of a decline in urinary estrogen (Burns, 1973). Blask (1984) has reviewed the role of melatonin in the clinical treatment of malignancy. He cites DiBella and Starr as achieving inhibitory clinical results in a variety of tumors.
In relation to endocrine action, Symthe and Lazarus (1974) have given 0.5 gms of melatonin for 2 doses, 30 minutes apart with a reported melatonin related rise in growth hormone.
Melatonin has been used in veterinary medicine in the treatment of acanthosis nigricans in dogs. This disease is associated with thickening of the skin, pigmentation and pruritus. Rickards (1965) and Kirk (1979) have successfully treated canine acanthosis nigricans by subcutaneous injection utilizing 2 mg injections of melatonin for daily and extended weekly treatment periods.
In regard to local modulation and inhibition of steroid synthesis, melatonin on in vivo and in vitro treatment has shown in vivo and in vitro inhibition of testicular synthesis from cholesterol and pregnenolone precursors of testosterone and androstenedione synthesis in the rat testes (Peat and Kinson, 1971).
The inhibiting effects of melatonin on testicular function have been associated with stimulation of delta-4-reductase in rat liver and hypothalamus (Frehn et al., 1974). Melatonin was found to specifically increase the 5-alpha reductase of seminiferous tubules for both progesterone and testosterone. Melatonin decreased androgen synthesis in both testicular interstitial cells and tubules (Ellis, 1972). Similar increases in 5 alpha reductase activity in rats by melatonin have been observed on adrenal cortical function (Ogle and Kitay, 1977).
Melatonin reduced accessory sexual organ size in pinealectomized male rats kept in constant darkness without inhibiting testosterone metabolism leading the authors (Shirama et al., 1982) to suggest that melatonin is possibly acting at the tissue level to reduce the number of androgen receptors and/or the susceptability to androgen.
Orally administered, melatonin was found to lower ventral prostate and seminal vesicle weight and the 3/beta-hydroxysteroid oxidoreductase was increased but not the 5 alpha reductase in the ventral prostate and seminal vesicles of pinealectomized rats (Horst et al., 1982). The authors felt that this reflects on increased androgenic catabolism resulting in prostatic involution. The effects of melatonin on prostatic androgen receptors can depend on the age of the animal and light cycle exposure (Moeller et al., 1983).
Melatonin in vitro when combined with chorinonic gonadotrophin or ovine luteinizing hormone increased the secretion of estrogens and progesterone in isolated granulosa cells of the rat. Melatonin, in relation to ovarian function, showed a progonadal trophic effect (Fiske et al, 1984).
In regard to local stimulation of estrogen receptor availability by melatonin in cutaneous areas of androgenic and estrogenic hormone sensitivity. There is evidence that melatonin increases cytoplasmic estrogen receptor activity in hamster uteri and similar effects have been observed in estrogen receptor binding activity in human breast cancer cells (Danforth et al., 1983).
Other reviews of the physiological role of melatonin are found in:
G. M. VAUGHN et al., titled "Evidence for a pineal-gonal relationship in the human", published in Prog. Reprod. Biol Vol. 4, pp. 191-223, 1978.
H. L. JUDD, titled "Biorhythms of gonadotrophins and testicular hormone secretion", published in Endocrine Rhythms, 1979.
D. P. CARDINALI et al, titled "Melatonin action: sites and possible mechanisms in brain", published in "The pineal gland and its endocrine role", J. AXELROD, F. FRASCHINI and G. P. VELO, eds. Proc. Nato Adv. Study, Erice, Italy, pp. 551-575, Plenum Press, New York, 1982.
R. J. WURTMAN, et al., titled "The secretion and effects of melatonin in humans", published in "The pineal gland and its endocrine role", J. AXELROD, R. FRASCHINI and G. P. VELO, ed. Proc. nato Avd., Erice, Italy, pp. 551-575, Plenum Press, New York, 1982.
The Third Colloquim of the European Pineal Study Group, PECS 1984, published in EPSG Newsletter of August, 1984.
R. J. Wurtman et al, entitled "Physiological Control of Melatonin Synthesis and Secretion: Mechanism Generating Rhythms in Melatonin, Methoxytryptophol, and Arginine Vasotocin Levels and Effects on the Pineal of Endogenous Catecholamines, The Estrous Cycle, and Environmental Lighting", J. of Neural Transmission, Suppl. 13, 59-70 (1978).
Ivor Smith, entitled "Indoles of Pineal Origin: Biochemical and Physiological Status", Psychoneuroendocrinology, Vol. 8, No. 1, pp. 41-60 (1983).
Surprisingly, none of the prior art studies are concerned with the dermatological effects of the administration of melatonin to a human host. Moreover, there have been no previous studies regarding the topical application of melatonin, its homologues or derivatives for humans. The prior art studies do indicate that the compounds of the invention can be safely administered to humans in the treatment of various diseases.